Sensor arrays, in particular with acoustic sensors, are of growing importance for a plurality of applications. In the field of mobile communication, for instance, where mobile phones are increasingly equipped with high power central processor units and powerful digital signal processors, a multitude of new features seems possible with advanced sensor arrays.
Audio conferencing devices rely on microphone arrays, hidden in the device, the arrays allowing for speaker tracking, speech enhancement, acoustic echo cancellation and everything needed for a hands-free conference call in a multi-speaker, noisy and reverberant environment. One example for such a device is the ‘Life Size Phone’ (http://www.lifesize.com/downloads/pdf/datasheet_phone.pdf, accessed on 27 Sep. 2007), an audio conference phone with a circular microphone array with 16 embedded microphones.
However, such devices are usually large and heavy and at the moment not suitable for use in mobile devices. This is due to the fact that commercially available sensor-arrays are up to now limited by their size and spatial sensitivity.
These two restrictions are however strongly dependent on physical properties of the signal of interest (wavelength). The size of a microphone array is defined by the frequency range of the signals to be processed and by the desired spatial resolution, thus not allowing the miniaturization of the size of those arrays. While the individual sensor elements/microphones of an array can be miniaturized, the geometrical distances among these sensor elements can not be reduced without affecting its spatial resolution capabilities for a given frequency range. Therefore, microphone arrays have not been included with mobile devices so far.